chore: add ruff linter and code formatter

[evansims]

Description

This pull request does not include any functionality changes. It introduces a faster and more streamlined linter and code formatted tool and applies some suggested code formatting rules.

Changes include:

• Updates the linter and code formatting tools used.

  • Adds the ruff linter and code formatted tool.
  • Removes the (now redundant) pyupgrade, isort, autoflake and black tools.
  • Replaces the previous setup.cfg file with a modern pyproject.toml equivalent.

• Applies improvements suggested by the tool:

  • Whitespace improvements.
  • Removal of unused imports.
  • Adds __all__ definitions to the __init__.py files as a best practice for exposing the SDK's public API to developer IDEs.

• Fixes a few minor issues in the examples and unit tests I identified while working on updating things:

  • Fixes the examples' setup.py files using incorrect header comment blocks.
  • Fixes minor issues identified in the example apps, like unused variable assignments.
  • Fixes a duplicately named unit test in api_test, which may have caused test_500_error_retry not to be run as intended.

• Ensures the partial_header block is imported in all Python source files.

References

Please review DXAZT-368 for additional context.

Generated from: openfga/sdk-generator#478

Review Checklist

• I have clicked on "allow edits by maintainers".
• I have added documentation for new/changed functionality in this PR or in a PR to openfga.dev [Provide a link to any relevant PRs in the references section above]
• The correct base branch is being used, if not main
• I have added tests to validate that the change in functionality is working as expected

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 95.23810% with 1 line in your changes missing coverage. Please review.

Project coverage is 69.58%. Comparing base (28945cb) to head (2ec56b1).

Files with missing lines	Patch %	Lines
openfga_sdk/exceptions.py	0.00%	1 Missing ⚠️

❌ Your project status has failed because the head coverage (69.58%) is below the target coverage (80.00%). You can increase the head coverage or adjust the target coverage.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #166      +/-   ##
==========================================
+ Coverage   69.56%   69.58%   +0.01%     
==========================================
  Files         135      135              
  Lines       10857    10864       +7     
==========================================
+ Hits         7553     7560       +7     
  Misses       3304     3304              

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